1. Technical Field
The technology herein relates to a development device using a two-component developer, more specifically, to a development device that develops an electrostatic latent image on a latent image carrier such as a photoconductor drum by supplying a two-component developer thereto.
2. Description of Related Art
In an image forming apparatus using electrostatic electrophotography, generally, steps of charging, exposure, development, image transfer, cleaning, charge removal and fixing are continuously performed. In such an electrostatic electrophotographic image forming apparatus, in forming an image, for example, the surface of a photoconductor drum being rotated is uniformly charged by a charging device, and then, a laser beam is selectively applied to the charged surface of the photoconductor drum by an exposure device, thereby forming an electrostatic latent image. Then, the electrostatic latent image on the surface of the photoconductor drum is developed by a two-component developer supplied from a development device, thereby forming a toner image corresponding to the electrostatic latent image. The toner image formed on the surface of the photoconductor drum is transferred onto a recording medium by a transfer device, and then, fixed onto the recording medium by being heated by a fixing device. The residual toner remaining on the surface of the photoconductor drum is removed by a cleaning device and collected in a predetermined collection device. The cleaned surface of the photoconductor drum has its residual charge removed by a charge removal device to be ready for the next image formation.
As the developer for developing the electrostatic latent image on the surface of the photoconductor drum, a single-component developer using only toner or a two-component developer consisting of toner and carrier is generally used. The single-component developer which uses no carrier has an advantage such that the structure of the development device is simple because a stirring mechanism for uniformly mixing toner and carrier is not required. However, it has a defect such that the charging amount of the toner is not easily stabilized. On the contrary, the two-component developer is excellent in the stability of the charging amount although it requires a stirring mechanism for uniformly mixing toner and carrier. Therefore, the two-component developer is generally used for high-speed image forming apparatuses and color image forming apparatuses.
A development device using the two-component developer generally includes a development tank, a stirring member, a development roller incorporating a magnetic member, and a restricting member. The development tank rotatably supports the stirring member and the development roller, and stores therein the two-component developer consisting of toner and carrier. The development roller rotates while carrying the two-component developer in a layer on its surface. The restricting member restricts the thickness of the developer layer carried on the surface of the development roller to a predetermined thickness to thereby supply a fixed amount of two-component developer to the surface of the photoconductor drum. The stirring member conveys the two-component developer toward the development roller while uniformly stirring it so that the mixture ratio (toner density) between toner and carrier in the development tank is constant.
However, when a multiplicity of document images where the image density is uneven are continuously printed, since the toner in the development tank is locally consumed, the toner density becomes uneven in the axial direction of the development roller. With respect to this problem, for example, Japanese Patent Application Laid-Open No. S62-217275 (1987) discloses a development device provided with a tubular developer conveyance path having therein a conveyance screw that conveys the two-component developer in the axial direction of the development roller in order to eliminate the toner density unevenness by uniformly dispersing the two-component developer in the development tank.